Modeling methods for tightly packed granular fuel

The paper investigates methods for modeling the neutronic behavior of fuels with Stochastic Granular Structures (SGS) to a high degree of fidelity and validates the models against equivalent homogenized cases. Granular fuels have recently been the subject of renewed attention due to their many attractive properties and their design flexibility. However, many fuels considered cannot reach high packing fractions, thus limiting their power density and heavy metal inventory. Developing and modeling fuels with higher packing fractions is therefore very desirable. An algorithm was developed to closely replicate tightly-packed structures within a cylindrical container. MCNP6 simulations were carried out using the obtained sphere coordinates and different metrics obtained were compared to homogenized models as well as models with simpler arrangements. The results were in good agreement and validate employing this SGS modeling method when a more exact representation of the microstructure is required.